Differential and Selective Media

What is the methyl-red test?

is differential in that it distinguishes between organism that can and cannot ferment glucose by means of mixed-acid fermentation

What is a durham tube?

Durham tubes are used to detect the production of gas by the microorganisms.

What is contained in the MacConkey agar?

Dyes and salts to inhibit the growth of Gram POSITIVE bacteria.

What is Carbohydrate Broths with Durham Tubes?

Carbohydrate broths with inverted durham tubes represent a differential test for the ability to ferment a variety of carbohydrates

What make citrate test positive?

Citrate-positive organisms are detected by a color change from green to blue media.

How can you tell if the coagulase test is positive?

Coagulase-positive will clump (clot) in the presence of rabbit plasma

What is a positive mannitol salt agar?

Colonies will turn yellow.

What is the difference between aerobes and facultative anaerobes?

Facultative anaerobes CAN make ATP even if oxygen isn't present, but aerobes cannot make ATP when oxygen is not present.

What is the Hektoen Enteric Agar?

HE agar is both a selective and differential type of agar. It is used to isolate and differentiate the Salmonella and Shigella genera of species from other enteric microorganisms

What is hemolysis?

Hemolysis is the destruction of red blood cells.

What does IMViC mean? Why are these tests usually performed?

IMViC stands for specific tests. These tests include "I" for indole test, "M" for methyl red test, "V" for Voges- Proskauer test, and "C" is for citrate test. These tests are usually performed to distinguish between the Enterobacterialis order of bacteria.

What makes an indole test positive?

If the layer containing the reagent turns red

How can you identify a positive catalos test?

It can be identified by dropping 3% hydrogen peroxide onto a slide containing a sample of the bacteria. The hydrogen peroxide will bubble if the microorganism is catalase-positive because you are seeing the oxygen bubbles produced by the reaction.

How is the bile agar selective?

It contains bile which inhibits the growth of gram POSITIVE

Bile agar is also differential media because?

It distinguishes between the ability of an organism to hydrolyze esculin.

What is a blood agar?

It is a type of enrichment and differential media. It is used for the isolation and cultivation of fastidious bacteria

What is a mannitol salt agar?

It is both a selective and differential type of agar used to isolate and distinguish among the various Staphylococci genera of bacteria

Sample from a patient will often be a?

Mixed culture

If the bile agar turns brown what could that mean?

Organisms that are able to hydrolyze esculin produce esculetin

What is positive fermentation in MacConkey agar look like?

Red/Purple colonies

What is the purpose of differential media?

Differential media helps you distinguish between groups of organisms that are related. You can often tell the difference by color or colonies.

What is the catalase test?

The catalase test is a differential test to distinguish between organisms that can and cannot produce the enzyme catalase

What is the Triple Sugar Iron Slant?

a differential test used to distinguish among the Enterobacteriales order of bacteria

What is the The Coagulase Test?

a differential test used to distinguish between organisms that can and cannot produce the enzyme coagulase

What is the Citrate Test?

a differential test used to distinguish between organisms that can and cannot use citrate as its sole carbon source

What is the indole test?

a differential test used to distinguish between those organisms that can or cannot digest the amino acid tryptophan to indole and other products using the enzyme tryptophanase

What is a pure culture?

A pure culture is a species isolated in one spot.

What is a Bile Esculin Agar?

A selective type of media used to isolate and cultivate the various Enterococcus species

What is a chocolate agar?

A type of enrichment media used for the isolation and cultivation of fastidious bacteria, such as the Neisseria and Haemophilus genera of species

How do can you tell the difference alpha beta and gamma in the blood agar?

Alpha has a green zone around it Beta has clear halos around the colonies Gamma has no color change

How is the MacConkey agar differential?

Because it distinguishes between the ability of an organism to ferment lactose.

Why is mannitol salt agar a differential type of media?

Because it distinguishes between the ability of an organism to ferment mannitol.

What does negative fermentation in Hektoen Enteric Agar create?

Blue to green colonies and no color change in the media

What is the MacConkey agar?

Both a selective and differential type of agar used to isolate and distinguish among the Enterobacteriales order of bacteria

What is the purpose of selective media?

The purpose of selective media is to isolate specific types of bacteria. Selective media contain chemicals that kill off some bacteria while helping other bacteria thrive.

What makes Voges-Proskauer test positive?

The reagents will react with the acetoin in the medium to produce a red color

What are fastidious bacteria?

They are bacteria that have complex nutrient needs. This kind of bacteria can only grow if a certain type of nutrient are included.

What are enteric bacteria?

This bacteria is harmless flora that is usually in the "gut" or intestines.

What is the coagulase test mainly used for?

This test is used mainly to distinguish between Staphylococcus aureus and other Staplylococci species.

What IMVIC series test used for?

To distinguish among the Enterobacteriales order of bacteria.

Why would you stab the media in a slant, such as a TSI slant?

To inoculate the media and depending on the situation, the stab will turn colors.

What is positive outcome in the Carbohydrate Broths with Durham Tubes look like?

Turns from pink to yellow

What does positive fermentation in Hektoen Enteric Agar create?

Yellow or orange colonies and media

What makes a methyl-red test positive?

by a color change in the media from yellow to red

How do you determine if the oxidase test is positive?

by adding tetramethyl-ρ-phenylediamine to a slide containing a sample of the bacteria. A purple color change indicates an oxidase-positive test

What is in the Hektoen Enteric Agar?

contains dyes and bile salts that inhibit the growth of Gram POSITIVE

What is The Oxidase Test?

differential test distinguishing between those microorganisms that can and cannot produce the enzyme oxidase

What is the Voges-Proskauer test?

distinguishes between organisms that can and cannot ferment glucose to acetone. The production of acetoin is detected by the addition of α−napthol and KOH (potassium hydroxide) to the media after incubation of the organism